Add Agent object

This adds an object interface for the AgentBuild entity we store
in the database.

Related to blueprint compute-manager-objects-juno
Related to blueprint virt-objects-juno

Change-Id: Idf9b4f025d234dce5bbc8f728b5e0900cf9e1e42
Object-ify xenapi driver's use of agent_build_get_by_triple()

This makes the xenapi driver use the new Agent object instead of
making a VirtAPI/conductor raw call back to the database.

Related to blueprint virt-objects-juno

Change-Id: I8498c6f3e2fa5d614ac301402d2be778e5edb74e
Deprecate and remove agent_build_get_by_triple()

This method was only used in the xenapi driver, which has since been
converted to use Objects. This removes the call from VirtAPI, the
conductor API, and deprecates it from conductor manager.

Related to blueprint compute-manager-objects-juno

Change-Id: I43b8c4bc201361ce79d56cac91a8944d18c03ab2
Use default rpc_response_timeout in unit tests

During running of tox the system can timeout on slower systems.
We have seen this occur in our internal tests and have seen
better results when we increased the api timeout from 15 to 60
seconds.  This can be used until faster hardware is availale
or a better fix is proposed.  Andrew Laski first proposed
this fix.

Closes-Bug: 1311778

Change-Id: I33da328e7bea8fbdde3f01ee0147b4c5a3a278d2
effectively disable libvirt live snapshotting

As being seen in the gate, libvirt 1.2.2 doesn't appear to actually
handle live snapshotting under any appreciable load (possibly
related to parallel operations). It isn't a 100% failure, but it's
currently being hit in a large number of runs.

Effectively turn this off by increasing the
MIN_LIBVIRT_LIVESNAPSHOT_VERSION to something that doesn't yet
exist. This can get us back to a working state, then we can decide
if live snapshotting is something that can be made to actually work
under load.

DocImpact

Related-Bug: #1334398

Change-Id: I9908b743df2093c8dd2723af89be51630eafc99f
Merge "effectively disable libvirt live snapshotting"
Merge "Use default rpc_response_timeout in unit tests"
Merge "Add Agent object"
Merge "Object-ify xenapi driver's use of agent_build_get_by_triple()"
Merge "Deprecate and remove agent_build_get_by_triple()"